topic Re: Virtual-chassis qfx5100 Switch Oversubscription in Ethernet Switchinghttps://forums.juniper.net/t5/Ethernet-Switching/Virtual-chassis-qfx5100-Switch-Oversubscription/m-p/292225#M14250
<P>If you really have the need for a lot of east-west (probably server) traffic, then VCF (or some type of Fabric solution) is probably a better solution to consider. &nbsp;If the traffic is more north-south, then the oversubscription for a VC is more related to uplink capacity, then VC capacity. &nbsp;Now you can make a VC type fabric with upto 7 x QFX5100s and ensure the total oversubscription is 2:1 but creating something like my [very crude] drawing, but for traffic between any 2 switches the oversubscription could be worse case 12:1, if all 48 input 10GE wanted to talk to interfaces on only one other switch. &nbsp;Therefore we you physically locate your servers within a fabric could well matter.</P>
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<P>Hope this helps. &nbsp;I hope the drawing comes through, is readable and makes sense. &nbsp;For the 7 node VC "fabric" all 6 x 40GE ports would need to enabled as VCP interfaces.</P>
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<P>&nbsp;</P>Mon, 23 May 2016 23:33:18 GMTrccpgm2016-05-23T23:33:18ZVirtual-chassis qfx5100 Switch Oversubscriptionhttps://forums.juniper.net/t5/Ethernet-Switching/Virtual-chassis-qfx5100-Switch-Oversubscription/m-p/292198#M14249
<P>Hi All,</P>
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<P>During my studies about QFX-5100-48T virtual chassis I noted that there is a kind of lack in the documentation about the switch over-subscription's topic.</P>
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<P>The 2 sets of built-in interfaces on QFX-51000-48T, 48 10GbE (connecetd to end hosts) and 6 40GB (uplink) can offer a switch-oversubscritpion of 2:1, (480Gb : 240Gb). So far so good.<BR />Jumping now on virtual-chassis topic (please note I am not talking about virtual chassis fabric)I further read that the traffic going from one switch to another in a ring topology is subject to nondeterministic over-subscription, depending on how many devices are between the source and the destination.<BR />My question now is: how can I compute the switch over-subscription in case of a virtual-chassis with 10 Node's members?<BR />If the books mentions non-deterministic over-subscription, is it really impossible to analise or plan the performance, in terms of over-subscription?</P>
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<P>Thanks for reading my doubts.</P>
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<P>&nbsp;</P>Mon, 23 May 2016 19:01:23 GMThttps://forums.juniper.net/t5/Ethernet-Switching/Virtual-chassis-qfx5100-Switch-Oversubscription/m-p/292198#M14249FabNewCert2016-05-23T19:01:23ZRe: Virtual-chassis qfx5100 Switch Oversubscriptionhttps://forums.juniper.net/t5/Ethernet-Switching/Virtual-chassis-qfx5100-Switch-Oversubscription/m-p/292225#M14250
<P>If you really have the need for a lot of east-west (probably server) traffic, then VCF (or some type of Fabric solution) is probably a better solution to consider. &nbsp;If the traffic is more north-south, then the oversubscription for a VC is more related to uplink capacity, then VC capacity. &nbsp;Now you can make a VC type fabric with upto 7 x QFX5100s and ensure the total oversubscription is 2:1 but creating something like my [very crude] drawing, but for traffic between any 2 switches the oversubscription could be worse case 12:1, if all 48 input 10GE wanted to talk to interfaces on only one other switch. &nbsp;Therefore we you physically locate your servers within a fabric could well matter.</P>
<P>&nbsp;</P>
<P>Hope this helps. &nbsp;I hope the drawing comes through, is readable and makes sense. &nbsp;For the 7 node VC "fabric" all 6 x 40GE ports would need to enabled as VCP interfaces.</P>
<P>&nbsp;</P>
<P>&nbsp;</P>Mon, 23 May 2016 23:33:18 GMThttps://forums.juniper.net/t5/Ethernet-Switching/Virtual-chassis-qfx5100-Switch-Oversubscription/m-p/292225#M14250rccpgm2016-05-23T23:33:18ZRe: Virtual-chassis qfx5100 Switch Oversubscriptionhttps://forums.juniper.net/t5/Ethernet-Switching/Virtual-chassis-qfx5100-Switch-Oversubscription/m-p/292253#M14251
<P>Hallo,</P>
<P>&nbsp;</P>
<P>Thanks for answering to my question.</P>
<P>If I got you correctly you are saying that the only topology able to ensure a 2:1 oversubscription is a full mesh with a maximum of 7 node in the VS. Is that correct?</P>
<P>If yes, this means that can&nbsp; a ring topology not guaranteee a 2:1 oversubscription?</P>
<P>More, if I am using a number of node greater than 7 how is the oversubscription affected (in full mesh topology)?</P>
<P>You can erasily understand that I am trying to figure out if here is question of topology, number of nodes and if some math could help in doing some pre-design plan.</P>
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<P>Thanks.</P>Tue, 24 May 2016 08:06:38 GMThttps://forums.juniper.net/t5/Ethernet-Switching/Virtual-chassis-qfx5100-Switch-Oversubscription/m-p/292253#M14251FabNewCert2016-05-24T08:06:38ZRe: Virtual-chassis qfx5100 Switch Oversubscriptionhttps://forums.juniper.net/t5/Ethernet-Switching/Virtual-chassis-qfx5100-Switch-Oversubscription/m-p/292401#M14255
<P>The usual answer is to go leaf - spine rather than full mesh. &nbsp;In order to guarantee 2:1 oversubscription in a 7 switch fabric, you'd have to get 2 spine switches (QFX5100-24Q), and run 3 uplinks out of each leaf into each spine. &nbsp;The question is if you need 2:1. &nbsp;You may only need 4:1 or 6:1.</P>
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<P>I don't think you can guarantee a 2:1 oversubscription in a ring given that the bandwidth of your 6 uplinks&nbsp;is a shared resource across multiple switches, and though there may be a way to figure out the oversubscription ratio between two given specific hosts, I think it would be very complicated, and would not be consistent oversubscription across all hosts. &nbsp;It would be affected by how much traffic is going east vs west, and the number of switch hops between any two given hosts.</P>Thu, 26 May 2016 19:54:51 GMThttps://forums.juniper.net/t5/Ethernet-Switching/Virtual-chassis-qfx5100-Switch-Oversubscription/m-p/292401#M14255JoelMcCotter2016-05-26T19:54:51ZRe: Virtual-chassis qfx5100 Switch Oversubscriptionhttps://forums.juniper.net/t5/Ethernet-Switching/Virtual-chassis-qfx5100-Switch-Oversubscription/m-p/292402#M14256
<P>Agree with this response. &nbsp;To decrese potential oversubscription is a ring, only options are decrease the inputs or increase the ring bandwidth, if possible.</P>Thu, 26 May 2016 20:05:20 GMThttps://forums.juniper.net/t5/Ethernet-Switching/Virtual-chassis-qfx5100-Switch-Oversubscription/m-p/292402#M14256rccpgm2016-05-26T20:05:20Z